Zhicao Feng

Effect of Surface Pretreatment on Galvanic Attack of Coated Al Alloy Panels

A test assembly consisting of a coated and scribed aluminum alloy 7075-T6 panel galvanically connected to uncoated through-hole noble fasteners has recently been utilized to quantify corrosion atta...

Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 2—Measurement of Galvanic Interaction

A test sample incorporating a painted Al alloy panel, uncoated through-hole fasteners, and scribes has recently been shown to provide an accelerated response during atmospheric corrosion testing in...

Friction Stir Welding of Al Alloy 2219-T8: Part I-Evolution of Precipitates and Formation of Abnormal Al2Cu Agglomerates

Friction stir welding was performed on AA2219-T8 plates with 6.31 wt pct Cu. The thermal cycles were measured in different regions of the joint during welding. Differential scanning calorimetry and transmission electron microscopy were utilized to analyze the evolution of precipitates in the joint. The relationships between welding peak temperature, precipitate evolution, and microhardness distribution are discussed. The temperature in the heat-affected zone (HAZ) ranged from 453 K to 653 K (180 °C to 380 °C). The θ″ and some θ′ phases redissolved into the HAZ matrix, while the rest of the θ′ phases coarsened. In the thermomechanically affected zone (TMAZ), the temperature range was from 653 K to 673 K (380 °C to 400 °C), causing both θ″ phase and θ′ phase to redissolve. In the weld nugget zone (WNZ), all the θ″, θ′, and some of the θ phase (Al2Cu) redissolved. Abnormal θ particles were observed in the WNZ, including agglomerated θ with sizes around 100 to 1000 µm and a ring-shaped distribution of normal size θ particles. The formation of abnormal θ particles resulted from metal plastic flow during welding and the high content of Cu in AA2219. No abnormal θ particles were observed in joints of another AA2219 plate, which had a lower Cu content of 5.83 wt pct.

Effect of Precipitate Evolution on the Pitting Corrosion of Friction Stir Welded Joints of an Al-Cu Alloy

The evolution of precipitates on the top surface of a friction stir welded AA2219-T8 joint was characterized using scanning electron microscopy and transmission electron microscopy. The pitting cor...

Galvanic Attack of Coated Al Alloy Panels in Laboratory and Field Exposure

A galvanic test panel design incorporating a painted and scribed Al alloy panel and uncoated through-hole noble fasteners has recently been utilized to compare effects of different surface pretreat...

Friction Stir Welding of Al Alloy 2219-T8: Part II-Mechanical and Corrosion

In Part I of this series, abnormal agglomerations of θ particles with size of about 100 to 1000 µm were observed in friction stir welded AA2219-T8 joints. In this work, the effects of these agglomerated θ particles on the mechanical and corrosion properties of the joints are studied. Tensile testing with in situ SEM imaging was utilized to monitor crack initiation and propagation in base metal and weld nugget zone (WNZ) samples. These tests showed that cracks initiated in the θ particles and at the θ/matrix interfaces, but not in the matrix. The WNZ samples containing abnormal agglomerated θ particles had a similar ultimate tensile stress but 3 pct less elongation than other WNZ samples with only normal θ particles. Measurements using the microcell technique indicated that the agglomerated θ particles acted as a cathode causing the dissolution of adjacent matrix. The abnormal θ particle agglomerations led to more severe localized attack due to the large cathode/anode ratio. Al preferential dissolution occurred in the abnormal θ particle agglomerations, which was different from the corrosion behavior of normal size θ particles.